EP0085582A1

EP0085582A1 - Cathodic protection using conductive polymer concrete

Info

Publication number: EP0085582A1
Application number: EP83300579A
Authority: EP
Inventors: Kenneth C. Clear; Yash P. Virmani; John Bartholomew
Original assignee: Harco Corp
Current assignee: Harco Corp
Priority date: 1982-02-05
Filing date: 1983-02-04
Publication date: 1983-08-10

Abstract

An impressed current cathodic protection system for the reinforcing steel in concrete. Current is carried by a polymer concrete (16) which contains calcined fluid petroleum coke particles: the cured polymer concrete has a resistivity of less than 5 ohm-cm, which eliminates the need for large quantities of material and excessively high voltage in the system.

Description

The present invention is a polymer concrete that can be applied to the surface of a bridge deck or other concrete structure and carry an impressed current to protect the reinforcing steel from corrosion. This requires that the polymer first be compatible with the concrete. A primary area of compatibility is coefficient of thermal expansion; if the coefficient of thermal expansion of the polymer is different from that of concrete, the polymer must be sufficiently flexible to dissipate thermal stresses. As an example of this, a certain rigid polymer was used to attach lane markers to a concrete highway. The coefficient of expansion of the polymer was different from that of concrete, and the cured polymer was too hard to stretch or compress to absorb the difference in expansions. As a result, after a period of months the polymer, which bonded firmly to the concrete, broke the layer of concrete under it away from the rest of the concrete; the lane marker thus was loose on the highway, still attached to the thin layer of concrete that it was initially applied to.
Another requirement is that the cured polymer be able to withstand the rigors of traffic driving over it day after day. This requires that it retain some flexibility when subjected to cold temperatures so that it does not crack when pounded by heavy trucks, but not become too soft in summer.
Another requirement is that the polymer bond to the concrete and not be loosened by the freeze-thaw cycles that it is ultimately exposed to in winter.
As stated earlier, the purpose of the polymer is to carry current as part of a cathodic protection system for the reinforcing steel. A polymer is more desireable in this application than portland cement concrete, because the polymer is more resistant to acid attack. The prior art shows many examples of polymers that have conductive particles in them which are used as floor coverings for static electricity buildup suppression. It has been found that while these polymers may be effective in preventing static electricity buildup, they are sometimes totally unsuitable for use in the environment of the present invention, which is a bridge deck, roadway, or other reinforced concrete member. It has been found that when a sample of an epoxy is immersed in salt water, to simulate the conditions which exist in winter due to the presence of deicing chemicals on the bridge deck, and then used as a current-carrying part of an electric circuit, the chlorine that is generated destroys the epoxy. The test set-up put 1 amp of current at 6 volts through the conductive epoxy for two days, and the epoxy was destroyed by the chlorine formed. Thus the prior art does not recognise that epoxy, as opposed to polyester or vinyl ester, resins are destroyed when used to carry current in an environment that includes a chloride-containing salt.
Another requirement is that the cured polymer concrete have as low an electrical resistance as possible in order to reduce the voltage that has to be applied to it and/or the thickness of nabit. material.which must be used. The conductivity is primarily a function of the particles added to the polymer, although as will be shown applicants have found that the properties of the polymer itself play a significant role in this. The prior art shows many different types of particles that can be added to polyester and epoxy resins to get low resistance, but no examples were found of a cured polymer that was used to carry currents of the order of 1 amp or more and which had the extremely low resistance of the polymer of the present invention.
According to the present invention, there is provided a method of cathodically protecting reinforcing steel in concrete which includes impressing an electrical current from at least one anode to the reinforcing steel, characterized in that the anode is formed at least in part by mixing thoroughly a conductive particulate material and an uncured polymer resin selected from a group of polymer resins which compact the particulate material upon curing thus rendering the anode significantly more conductive, curing such polymer resin to form a cured polymer, and then impressing such current between the anode and reinforcing steel.
There is particularly disclosed herein a polyester or vinyl ester resin having carbon particles distributed within it which is used to carry electric current; the resin is applied to a bridge deck or other reinforced concrete structure and is used in an impressed current cathodic protection circuit as one of the current-carrying members. The resins have the proper physical properties which allow them to be used on portland cement concrete, and are very resistant to destruction by the acid and the chlorine gas formed when used in the presence of chloride-containing salts.
The invention will be better understood from the following non-limiting description of examples thereof given with reference to the accompanying drawings in which:-

Figures la, lb and lc show the placement of the conductive polymer on a road surface or bridge deck.
Figure 2 shows the deterioration of a sample of epoxy resin when used as described herein.
Figure 3 shows the location of the reinforcing steel in a test slab that the cathodic protection system of the present invention was tested on.
Figure 4 shows the location of the test points in the slab of Figure 3.
Figure 5 shows the placement of anodes in a section of bridge deck.
Figure 6 shows the performance of the cathodic protection system of Figure 5.
Figure 7 shows the placement of anodes in a system that did not utilize a conductive overlay.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Figure la shows a cross section of a bridge deck or roadway that has the present invention applied to it. The portland cement concrete portion 10 is of conventional construction, comprising portland cement concrete 12 with reinforcing steel members 14 within it. On top of this is placed a relatively thin (of the order 0.1 inch) layer of the polymer concrete 16 of the present invention having primary anodes 18 within it. Polymer concrete layer 16 is part of an impressed current cathodic protection system (not shown) which is designed to prevent the deterioration of the reinforcing steel members 14 within the portland cement concrete.
Figure lb shows an alternative method of placing anodes 18. In this method, slots 19 are cut in the existing surface and anodes 18 are placed in the slots. The slots are then filled with conductive polymer, and the surface is covered with a thin layer of conductive polymer as in Figure la or a coat of conductive paint may be applied as in the example of Figures 3 and 4. Conductive paint can be used where the surface is not subjected to abrasion from foot or vehicle traffic (the side of a retaining wall, for example).
Figure lc shows another alternative, the close spacing of anodes (primary anode (metal or carbon strand) and conductive polymer concrete) to eliminate the need for a continuous conductive layer on the surface.
As is well known in the art, the deterioration of the members 14 is due to the formation of natural electric currents which result from the penetration of chloride salts and the different electrical potentials along the members 14 within the portland cement concrete 12. Stopping of the deterioration can be achieved by impressing a current on the reinforcing steel and making all the steel in the concrete cathodic, thus neutralizing the naturally occurring electric currents.
Primary anodes 18 carry the impressed current, and polymer concrete 16 distributes this current evenly to the reinforcing steel of the bridge deck or roadway thus providing the "couple" between the existing concrete and the primary anode. It is obvious that primary anodes 18 could be incorporated within the body of portland cememt concrete 12 in new construction. Applicants' invention, however, is intended for use on existing structures; in these applications it is difficult or impossible to reconstruct the bridge or road, hence the impressed current carrying part of the circuit must be an overlay on the existing surface or in slots placed in the existing surface. Further, acid is formed near the primary anode 18. This will destroy the portland cement concrete, whereas the polymer concrete is immune to such destruction. Such acid attack of a portland cement based anode backfill material resulted in deterioration of the backfill and exposure of the anode wire in tests on large slabs and on bridge decks after only several months of use.
Although the prior art shows many examples of polymer concretes (i.e., cured polyester or epoxy resins) that have conductive particles in them and are stated to be used in seemingly analogous applications, applicants have found that most epoxy resins are destroyed when used to carry currents needed in cathodic protection systems. Figure 2 shows an example of this destruction. A sample of Niklepoxy concrete injection epoxy (product number 3 epoxy resin), manufactured by Rocky Mountain Chemical Co., P.O. Box 2494, Casper, WY 82602, was cast with copper wires in it as the primary anodes. It also contained calcined fluid petroleum coke (obtained from C.E. Equipment Co., IIattiesburg, MS 39401), the preferred particulate material for imparting electrical conductivity. After two days of carrying 1 amp of current at 6.0 volts while partially immersed in a solution of 3% sodium chloride (to simulate the conditions which result from the application of deicing chemicals in winter), the resin was in the condition shown.
The deterioration of the epoxy resin has been determined to be a result of attack by the nascent chlorine formed by the passage of current through the resin, the chlorine coming from the deicing salt in the water. Since existing bridge decks contain the chloride salt in the concrete already and will receive more salt to eliminate icing conditions in winter, a resin overlay or primary anode encapsulent will also be subject to this condition and clearly the epoxy resins are not suitable for use.
Polyester resins, by contrast, show little deterioration after 16 days under the same conditions of current and salt solution. Since this current level is much higher than would be used in practice, it is felt that the test shows that polyester resins are suitable for long-term use. Further, vinyl ester resins have been found to be even more resistant to degradation and thus can be used in high current density applications.
As stated above, calcined fluid petroleum coke is the preferred particulate material for imparting electrical conductivity. However, this material does not produce the desired results when used with all resins. For epoxies in general, the resulting conductivities were unacceptably high (from 30.7 to 5.5 million ohm-cm when mixed with calcined fluid petroleum coke). In another case, when calcined fluid petroleum coke was added to methyl methacrylate resin without any other aggregate such as sand, the resin did not set (harden). When sand or other fine aggregate was added along with the coke, the material became an insulator (it had a resistance in excess of 64 million ohm-cm). Applicants found one epoxy resin which gave marginally acceptable resistivity, Epi Rez 510 (made by Celanese Plastics and Specialty Co., 1065 West Hill Street, P.O. Box 8248, Louisville, KY 40208), which when mixed with toluene and a curing agent and coke gave a resistivity of 3-4 ohm-cm. However, as shown above, epoxy resins do not withstand the attack by chlorine gas which results from the passage of current in the presence of deicing chemicals.
Applicants have found that the preferred polymer resins and in particular the most preferred polyester and vinyl ester resins do not produce acceptably low resistivities when used with carbon additives other than calcined fluid petroleum coke. As the following table shows, the resistivity of a polyester resin polymer concrete varies considerably with the carbon additive:
In the above Table, item no. 3 is an example of the invention and the other items are for comparison to demonstrate the point mentioned above.
The reason that the preferred combinations work so much better than other combinations is thought to be a result of two things which combine in such a way that they reinforce each other. The first is that the calcined fluid petroleum coke absorbs approximately 18% resin; the second is that the preferred resins shrink as they harden. When these two effects are combined, the result is that the particles are pressed together in such a way that intimate particle to particle contact is achieved. The fact that conductivity is a function of particle to particle contact can be demonstrated; if the dry coke is tamped into a mold, it has a resistivity of 62.7 ohm-cm; if hand pressure is then applied to the coke, the resistivity drops to 3.84 ohm-cm, presumably a result of the greater contact pressure of the cured resin. Further evidence of this is the decrease in resistance of the preferred polyester resin as it cures, as shown in the following table:
In addition, continuity of the carbon with a particle, particle shape, and gradation also play important roles. Although the exact criteria for good conductivity are not known, applicants have found that only the calcined fluid petroleum cokes possess them.

Mix Trials and Resistivity Beams

Various mix trials were performed in a manner not open to the public to determine the resin and coke contents needed for trowelable and pourable conductive polymer concretes. Results indicated resin contents of 23% to 25% for a trowelable mixture with all fine coke aggregate, 35% for a pourable mixture with all fine coke aggregate, and 17% for a trowelable mixture with 52% natural sand and 48% fine coke by weight of total aggregate. Other mixes required resin contents between 17% and 35%. Table A provides the mix designs for each of five separate mixes.

Mix Properties

Mix 1 - Trowelable, mortarlike consistency with resistivity of about 1.4 ohm-cm and a unit weight of about 88 pounds per cubic foot (pcf).
Mix 2 - Pourable, mortarlike consistency with resistivity of about 2.5 ohm-cm and unit weight of about 87 pcf.
Mix 3 - Flowable, concretelike consistency with a resistivity of about 1.0 ohm-cm and a unit weight of about 91 pcf.
Mix 4 - Flowable, concretelike consistency with a resistivity of about 2.1 ohm-cm and a unit weight of about 101 pcf.
Mix 5 - Trowelable, mortarlike consistency with a resistivity of about 3.1 ohm-cm and a unit weight of about 108 pcf.

(102 x 356mm) Three inch by 4 inch x 14 inch_Abeams were made in.a manner not open to the public with each material and the resistivity of each cured polymer concrete was defined by measuring the 1000 cycle AC resistance, R, between two copper screens positioned exactly 2.00 inches apart within each beam. The R value is converted to resistivity by multiplying by an experimentally determined cell constant. The resistances and_Iesistivities defined for beams made with the subject invention are presented in Table B.
In summary, conductive concretes with electrical resistivities varying from 0.8 to 3.4 ohm-cm can be made using:

1. LB 183-13 Polyester Resin contents to 17 to 35 per cent and:
- All fine (DW2) coke as aggregate; or
- A mixture of fine (DW2) and coarse (SWK) coke as aggregate; or
- A mixture of fine (DW2) coke and quartz sand (up to
- a sand/coke ratio of 1 to 1) as aggregate; or
- A mixture of fine (DW2) coke, coarse (SWK) coke and concrete sand (up to a sand/coke ratio of 1 to 2) as aggregate.
2. LR 13468-120A and 13468-20B vinyl ester resin contents of 28 to 36 percent and all fine (DW1 or DW2) calcined fluid petroleum coke as aggregate.
3. Epoxy Resin (Epi-Rez 510 and Epi-Cure 8525) diluted with at least 50 percent toluene and the above mentioned aggregates.

Consistency of the mixture can be varied from stiff but trowelable to easily pourable.
The material may be colored gray with only a modest increase in resistivity.

Engineering Properties

The compressive strengths of the two trowelable mixes (mixes 1 and 5 in Table 1) were defined using 2 inch cubes and testing in accordance with ASTM. Results (each the average for two cubes) are given below:

Trowelable mix, all coke = 7460 psi
Trowelable mix, 52 percent sand and 48 percent
coke = 9550 psi
Stress-strain curves were defined during testing of each of the above cubes and the following modulus of elasticity results were obtained;
Trowelable mix, all coke = 3.3 x 10⁶ psi
Trowelable mix, 52 percent sand and 48 percent
coke = 5.0 x 10⁶ psi

Additionally, the cubes were weighed and the following unit weights resulted:

Trowelable mix, all coke = 88 pcf
Trowelable mix, 52 percent sand and 48 percent coke = 108 pcf
Several cubes were immersed in salt water for 21 days and the salt water absorptions were measured by weighing:
Trowelable mix, all coke = 0.23 percent absorption

Trowelable mix, 52 percent sand and 48 percent coke = 0.07 percent absorption.

20 ft² Cathodic Protection Trials Conducted in Secret

(a) With conductive paint

The conductive polymer concrete was utilized to embed platinum and niobium clad, copper core primary anode lines in slots placed in an existing 4 feet x 5 feet x 8.5 inch reinforced concrete slab. The top mat reinforcing steel in the slab was corroding due to the intrusion of chloride into the concrete during 7 years of daily salting. The polyester resin trowelable mix with all coke aggregate (Mix 1 in Table A) was utilized as the slot-fill material (slot size approximately 0.5 inch x 0.5 inch) and after set, a layer of conductive paint (Acheson Colloids Electrodag 188) was applied to the surface. The paint was omitted on small areas of the slab to facilitate potential measurements. Figures 3 and 4 provide a plan view of the surface of the slab showing top reinforcing steel locations, the rate of corrosion probe location, anode locations, and the locations of the unpainted spots used for potential measurements. The potentials were measured using portable copper/copper sulfate cells placed on the unpainted concrete.
The cathodic protection (CP) system was activated using anode 1 only and a constant current of 35 mA (1.75 mA/ft² of concrete surface; 9.9 mA/ft² of top mat rebar; and 3.5 mA/ft² of total rebar). System voltage was 2.0 volts and the concrete temperature averaged 18.3⁰C. Table C shows the electrical potentials of the top mat reinforcing steel before CP activation, the instant off potentials 30 minutes after activation, and the differences in potential due to CP. These data show conclusively that the steel can be polarized using this cathodic protection system. "Throwing power" of a single slot anode is at least 3 feet (the maximum length tested).
The cathodic protection system on this slab was operated at various currents and voltages for five months. A total of about 75 ampere- hours of current was passed without degradation of the conductive polymer concrete. Bond of the conductive polymer concrete to the portland cement concrete is excellent. Additionally, no large driving voltage increases have occurred during constant current tests, thus indicating that primary anode gas blockage is not a problem, even during a 2-day high current test when 300 mA was applied, and all top mat reinforcing steel was polarized to instant off potential more negative than -1.01 volts saturated Calomel Standard Electrode (CSE). The rate of corrosion probe in the slab has indicated a zero corrosion rate.

(b) With built-up conductive polymer concrete overlay.

Cathodic protection was applied to another 20 ft² slab using the conductive polymer concrete. Slab construction, reinforcement, slot size, primary anode material and locations, and previous exposure history were the same for this slab as for that described previously.
A layer of resin only was painted on the slot surfaces to guarantee good contact of the polymer concrete with the existing concrete, the anode wires were placed in the slots, and the slots were filled with Mix 2 from Table A. To prevent resin bleeding to the surface from creating a high resistivity layer, additional DW2 coke was sprinkled on the surface (to excess) while the concrete was curing.
The following day, the slab surface was sandblasted and a 4 layer built-up polymer concrete overlay was placed. In the built-up system, a layer of resin with additives is spread on the surface, aggregate is broadcast onto the resin and then the material is rolled. After this material has cured, the excess aggregate is removed and a second layer is applied in an identical manner. The first two layers of this overlay were made conductive through the use of Loresco DW2 coke as the sole aggregate. An angular quartz aggregate was used for the final two nonconductive layers.
Testing prior to the application of CP indicated that the overlay was indeed conductive. For example, the 1000-cycle AC resistance between the two metal anode wires was 2380 ohms when the slots were simply filled with dry DW2 coke. After filling the slots with conductive polymer concrete and placing the built-up overlay, the anode to anode resistance was 10.2 ohms.
The CP system was activated using anode 2 only and currents varying from 17 to 25mA. Two days later the current was increased to 30mA and the CP rectifier was set to constant current for 25 days. At that time, control at a constant voltage of 3.0 volts was initiated. Current output typically varied between 30 and 40mA depending primarily upon concrete temperature. Testing has repeatedly indicated that this CP system is functioning quite well. For example, the following data were obtained during depolarization tests (system current prior to shutdown was 38mA (1.9 mA/ft² of concrete surface; 10.7 mA/ft of top mat rebar; and 3.8mA/ft² of total rebar)):

Trial on a bridge deck section

The conductive polymer concrete cathodic protection system was installed on a ll3 ft² section of bridge deck which had been extracted from a 22-year old bridge deck that was being removed because of corrosion induced concrete damage. The slab was transported to Fairbank Highway Research Station and placed on 3-foot high posts. All exposed rebars on the slab edges were wired together to insure continuity and the edges were coated with 2 layers of epoxy paint. Cathodic protection instrumentation (reference cells, rate of corrosion probes and thermocouples) was then installed at the level of the top mat of reinforcing steel. The reference cells for this slab were silver/silver chloride rather than the copper/copper sulfate cells used previously.
Three primary anode wires were installed in slots in the slab surface using the pourable conductive concrete of mix 2 of Table A and the 4-layer built-up polyester polymer concrete overlay was placed over the entire slab. Figure 5 is a plan view of the slab with the position of all top mat reinforcing steel, anode lines and CP instrumentation shown. Installation procedures were identical to those used on the previous slab with the single exception that the original deck surface was scarified and sandblasted prior to overlay placement. Table D summarizes the electrical resistance data taken before, during and after system installation. Obviously, a very conductive slot fill and overlay resulted. For example, the 1000 cyele-AC resistance between anode 1 and anode 3 (15 feet apart) prior to overlay placement was 822 ohms, whereas this resistance the day after placement was 7.07 ohms.
The cathodic protection system was activated the following day. Static (before CP) electrical potentials indicated by the 4 silver-silver chloride reference cells are given below:
The system rectifier was TASC V automatic instant OFF potential controlled SCR rectifier. Only anode line 1 (on one edge of the slab) was activated and system control was obtained by presetting the desired reference cell 4 set potential at -0.78V (equivalent to -0.85V CSE). Cell 4 we_E used because it is the embedded cell positioned the greatest distance from anode 1 (12 feet). The system was then activated and within 3 minutes the desired set point was achieved. With the system operation at 4.0 volts and 0.35 amps the following instant OFF reference cell potential were recorded:
"TASC" is a trade name of Harco Corporation.
These data show conclusively that the system was functioning extremely well (over 350mV polarization in all instances). Anode 1 was then deactivated, and anode 2 (in the center of the slab) was briefly activated to confirm operation. After this test proved successful, anode 2 was deactivated and anode 3 (on the opposite end of the slab from anode 1) was activated; system control was transferred to reference cell 3, set at -0.78V silver. Instant OFF potentials (silver) 1 hour later and those the next morning are shown below, along with system operating voltage and amperage.
These data also indicate full cathodic protection has been achieved (all potentials equal to or more negative than -0.85V CSE (i.e. -0.78V silver) and more than 300 mV polarization from static).
The system remained under the above mode of operation for a week, after which it was turned off for the purpose of charting depolarization. System current varied between 0.18A and 0.35A to maintain set point. This is equivalent to current densities of 1.6 to 3.1 mA/ft² of concrete surface, 2.0 to 3.8 mA/ft² of total rebar and 4.8 to 9.4 mA/ft² of top mat rebar. Figure 6 shows the depolarization characteristics detected by the embedded reference cells. Again, these data indicate excellent cathodic protection.
In summary, the large scale bridge deck trial confirms that the subject conductive polymer concretes can be utilized to provide efficient impressed current cathodic protection. The date indicate that primary anode spacing of at least 26 feet will be possible. Also, chain-drag testing after overlay placement and a month later indicate it was properly bonded to the original deck surface.

(e) Non-overlay CP system, i.e. cathodic protection system.

Cathodic protection can be achieved without the use of a conductive overlay or coating of the anodes are spaced closely together. Another 4 feet by 5 feet by 8.5 inch slab, like those shown in Figures 3 and 4, was used to confirm this system. The cathodic protection system is contained in slots placed in the concrete surface. Figure 7 shows the locations of the 3/8 inch slots and the locations of the potential measurements. To minimize costs a platinum-clad wire was used as the transverse anode and carbon strands (2 Thornel 300, WYP 6 1/0 strands manufactured by Union Carbide Corporation, Danbury, Connecticut) were used as the longitudinal anodes. The vinyl ester conductive polymer concrete was then poured into the slots and silica sand was sprinkled on its surface to complete the CP system. To color match the conductive polymer concrete with the existing portland cement concrete, 0.7 percent titanium dioxide was blended with the calcined fluid petroleum coke; this produced a gray color in the polymer concrete. (Alternatively, the titanium dioxide could have been added to the resin). It should be noted that the titanium dioxide increases the resistivity of the polymer concrete; the last 2 items of Table B give an indication of the magnitude of the increase. The following polarization data confirm that cathodic protection of the top mat reinforcing steel has been achieved.
CP System: Non-overlay; grid of vinyl ester conductive polymer concrete (PC) in 3/8" square slots. Platinum clad wire in transverse slot; carbon strands in longitudinal slots. Installed and activated 9/4/81.

(d) Cathodic protection system with non-conductive overlay

Some bridge decks need an overlay to restore riding quality. Since civil engineering overlays with proven service history are sometimes preferred, another means of using this system to achieve cathodic protection was defined. It involves the placement of a cathodic protection system similar to that described in item (c) on the existing surface (rather than in slots) and then overlaying that with conventional portland cement concrete or other paving material. Alternatively, the system could have been placed in slots just as in item (e) and then the overlay placed on top.
Two slabs similar to the previous ones were used to determine the viability of this system. A grid of conductive polymer concrete lines was placed on the surfaces of the slabs at the same locations as the slots shown in Figure 7. The transverse line contained a platinized wire while the 5 crossing lines were composed of only conductive polymer concrete. The polymer concrete for one slab was polyester resin while that for the other slab was vinyl ester resin. Several days after placement of the polymer concretes, the slab with the polyester resin CP system was overlaid with 1.5 inches of latex modified portland cement concrete and the slab with the vinyl ester resin CP system was overlaid with 1.5 inches of conventional portland cement concrete. The following polarization data confirm that CP systems on both of these slabs are functioning properly; no delamination or other failures of the overlays has occurred.
CP System: Grid of polyester conductive polymer concrete lines applied to surface in 0.75" high and 1.5" wide strips and then overlaid with a 1.5 layer of .40 w/c latex modified concrete. CP system activated 8/5/81.
CP system: Grid of vinyl ester conductive polymer concrete lines applied to surface 0.5" high and 1" wide strips and then overlaid with a 1.5" lift of 0-0.45 w/c portland cement concrete. CP system activated 8/18/81.
Thus it will be seen that applicants have provided a cathodic protection system which stops the corrosion of the reinforcing steel in concrete; further, that the resin can be placed on less than the entire surface of the concrete (i.e. in slots cut in the surface, or strips of resin placed on the surface).
Although the present invention has been described with respect to a cathodic protection system for reinforcing steel, it is obvious that calcined fluid petroleum coke can be used as the particulate matter in any CP of the CP applications shown by the prior art wherein a normally non- conductive polymer is made conductive by the addition of particulate matter to the polymer.
In the following claims the words "resin" is intended to mean the resin itself plus all standard additives such as catalyst, coupling agent, wetting agent, etc.

Claims

1. A method of cathodically protecting reinforcing steel in concrete which includes impressing an electrical current from at least one anode to the reinforcing steel, characterized in that the anode is formed at least in part by mixing thoroughly a conductive particulate material and an uncured polymer resin selected from a group of polymer resins which compact the particulate material upon curing thus rendering the anode significantly more conductive, curing such polymer resin to form a cured polymer, and then impressing such current between the anode and reinforcing steel.

2. A method as set forth in claim 1 wherein said particulate material is calcined fluid petroleum coke.

3. A method as set forth in claim 1 wherein such resin is selected from a group of resins including polyester resins, vinyl ester resins, and diluted epoxy'resins.

4. A method as set forth in claim 1 wherein the cured polymer has a resistivity of from about 0.08 to about 14.0 ohm-cm.

5. A method as set forth in claim '1 wherein such anode includes a linear conductive strand.

6. A method as set forth in claim 5 wherein such linear conductive strand is carbonaceous fibers.

7. A method as set forth in claim 1 including the step of cutting a slot in the surface of the concrete, placing the uncured resin mixed with such particulate material in such slot, and curing the polymer resin in situ.

8. A method as set forth in claim 7 including the step of placing a current carrying member in said slot prior to placement of the uncured polymer resin mixed with the particulate material in such slot.

9. A method as set forth in claim 1 wherein such anode is placed over the surface of the concrete.

10. A method as set forth in claim 1 wherein a protective surface layer is placed on top of such anode.

11. A method as set forth in claim 1 wherein such anode is mixed and cured in situ.

12. A cathodic protection anode characterized in that it comprises a conductive polymer having a resistivity of from about 0.08 to about 14.0 ohm-cm.

13. An anode as set forth in claim 12 wherein said anode contains a mixture of a conductive particulate material and a resin which shrinks upon curing.

14. An anode as set forth in claim 13 wherein said resin is selected from a group of resins including polyester resins, vinyl ester resins, and diluted epoxy resins.

15. An anode as set forth in claim 13 wherein said conductive particulate is calcined fluid petroleum coke.

16. An anode as set forth in claim 12 wherein said anode includes a conductive linear strand.

17. An anode as set forth in claim 16 wherein said conductive linear strand is formed of carbonaceous fibers.